1. Field of the Invention
The present invention relates generally to a device with a beam structure, and a semiconductor device, and more particularly to the device and semiconductor device including a MEMS (Micro-Electro-Mechanical System) device.
2. Description of the Related Art
In recent years, the reduction in scaling of micromachine technology has constantly been progressing. The micromachine technology includes MEMS technology. The MEMS technology is a technology in which movable three-dimensional devices are finely fabricated using semiconductor process technologies.
As devices that are fabricated using MEMS technology, a variable capacitor, a switch, an acceleration sensor, a pressure sensor, an RF (radio frequency) filter, a gyroscope and a mirror device, for instance, have been principally researched and developed.
In a case where a beam is fabricated over a cavity using MEMS technology, it is a very important point how to suppress a warp occurring due to residual stress in a layer that constitutes the beam. For example, in the case of a MEMS variable capacitor, if a warp occurs in an electrode layer that constitutes the variable capacitor, a desired capacitance value could not be obtained. In addition, if a warp occurs in an actuator that moves the electrode layer, the capacitance value of the variable capacitor could not be varied at a desired voltage value.
Such the warp due to residual stress tends to occur in the case where the beam is formed of two or more layers. The reason is that it is difficult to equalize the values of residual stresses in the respective layers. For example, in the case of a piezoelectric type variable capacitor or switch, at least three layers need to be used in a piezoelectric actuator, and thus the warp tends to occur in particular. As a related technique, a technique relating to a warp of a piezoelectric actuator is disclosed (see Myeong-Jin Kim and Young-Ho Cho, “DESIGN, FABRICATION AND CHARACTERIZATION OF PIEZOELECTRIC MULTI-LAYER CANTILEVER MICROACTUATORS FOR THE MINIMUM INITIAL DEFLECTION”, Transducer '99, Jun. 7-10, 1999, pp. 1758-1761).